The present invention relates to low-halogen-content, thermoplastically processible polyurethane elastomers (TPU) to which a special 4-component additive mixture imparts an unexpectedly favorable combination of electrical surface properties, flameproof behavior and abrasion resistance.
It is known that a concentrate of antimony trioxide and brominated diphenyl ethers or polystyrene can be added to thermoplastic polyurethane elastomers (German Offenlegungsschrift No. 2,901,774). No examples of the flameproofing effect are given in this publication, nor is there any mention of phosphorous compounds and aluminum hydroxide.
In the case of polyurethane foams, examples of brominated phenoxy compounds and antimony trioxide are described in U.S. Pat. No. 3,971,760. Although aluminum hydroxide is mentioned, it is not a basic requirement for the flameproofing effect. The composition in question does not contain any chain-extending agents or phosphorus compounds.
Fire-retarding preparations based on phosphate esters and aluminum oxide trihydrate are described in German Offenlegungsschrift No. 2,263,005. Reference is made to a self-expanding polyurethane. Halogen compounds and antimony trioxide are not used. The abrasion resistance of the products is unfavorable.
The combination of silicon dioxide, antimony trioxide, bromine and phosphorus compounds has been described in connection with linear polyesters (German Offenlegungsschrift No. 2,242,509). Finely divided silicon dioxide in a quantity of from 5 to 12% by weight and preferably 5% by weight is essential to the disclosed effect, but reduces the abrasion resistance (and other strength properties) of the resultant polyurethane elastomers. This known combination does not contain the important synergist aluminum hydroxide.
None of these products is capable of being used to provide a thermoplastic polyurethane elastomer in such a way that a material produced therefrom has the particular combination of properties, such as high strength, good abrasion resistance, high tear propagation resistance, high flame resistance, stipulated by various standards, for example VDE 0472, coupled with improved electrical surface properties.